In many petroleum and chemical processes it can be desirable to use enriched oxygen instead of air. Examples of such processes include the Claus process for recovery of elemental sulfur from H2S containing streams, and the GTL process for producing liquid hydrocarbons from natural gas. Enriched oxygen (typically 30-80% O2) can improve process efficiency in several ways including elimination of inert N2 heating to process temperature and a reduction in flow volumes and equipment size. In such processes, the capital investments for the oxygen plant can be very large, often exceeding a ¼ or even ⅓ of the total plant costs. Thus, reducing or minimizing the cost of the air separation technology used to form enriched oxygen can provide a substantial benefit. In addition to investment, other considerations, such as energy requirements, plant footprint, process reliability and safety also contribute towards the selection of air separation technology.
The two current commercially used air separation technologies either use distillation of oxygen from nitrogen at cryogenic temperatures, or pressure (or vacuum) swing adsorption using a N2 selective adsorbent (the vacuum pressure swing adsorption (VPSA) process has mostly replaced the older pressure swing process in recent years).
Cryogenic air separation process permits a better economy of scale than the VPSA process. The capacity of a commercial VPSA unit is generally limited to less than about 200 tons per day (TPD) of oxygen whereas the capacities of cryogenic air separation units can be much higher and can approach 5000 TPD or even higher. Modern large scale plants generally require more than 1000 TPD of enriched oxygen. Thus, VPSA technology is at a disadvantage in large commercial plants because of its unfavorable economy of scale. In addition to an unfavorable economy of scale, the VPSA process also has a larger footprint and requires more maintenance because of the periodic frequent maintenance of the flow switching valves.
U.S. Patent Application Publication 2014/0175336 describes systems and methods for using rotary wheel sorption-desorption to separate CO2 from various streams, such as flue gas streams. The rotary wheel corresponds to a solid monolith that can selectively sorb CO2. Optionally, two or more rotary wheels can be used in conjunction so that, during various sorption and/or desorption steps, the output flow from a first wheel can be used as (at least part of) an input flow for a second wheel.
U.S. Pat. No. 8,974,576 describes a continuous or semi-continuous, cyclic, countercurrent sorption-desorption method for enhanced control, separation, and/or purification of CO2 gas from one or more sources of a mixture of gases through integrated use of solid monolithic sorbents having sorption selectivity for CO2.